Since its inception in 1984, the goal of the CSHL FACS Shared Resource has been to give Cancer Center members access to state-of-the-art flow cytometry equipment and support. The Resource has evolved with emerging technologies and changing research needs. In 1984, the primary use was separation of cells by DNA content or by expressed cell-surface antigens. The advent of fluorescent markers (such as the green fluorescent protein GFP) ushered in a new phase in FACS usage, as Cancer Center members used GFP to track transfected cells, and to isolate particular populations of cells from complex mixtures. Increases in the speed and efficiency of sorting by FACS have enabled completion of experiments that once would have been impossible or impracticalsuch as the isolation of large quantities of tumor or stem cells for genomic and genetic analyses. The recent introduction of the new generation of proteins that fluoresce in various colors and are less toxic than their predecessors, changed the requirements for flow cytometers and increased the demand for the Resource. In response to these demands, the FACS Shared Resource has undergone an extensive series of changesin location, instrumentation, and personneldesigned to expand FACS capabilities at CSHL, and improve the efficiency and reliability of flow cytometry for Cancer Center members.